I would add that the most powerful problem solving tool is to exclude things first, in order to narrow down the possibilities. If you're lucky you can exclude everyting that it could be, except one, and that is it! Usually you're not that lucky, but excluding the things it can't be can really speed up the process of finding the problem. I never read Sherlock Holmes, but I've been told that he said the same basic thing. My life has revolved around it.